An animal model of polydrug abuse will be developed to study drug interactions with behavior. Monkeys will be trained to emit lever-press responses for food or intravenous drug reinforcement. A multiple schedule of reinforcement will be used in which a period of available food reinforcement both precedes and follows a period of drug reinforcement. Prototype drugs from the following classes will be tested alone and in combination with narcotic analgesics: narcotic analgesics, narcotic antagonists, psychomotor stimulants, sedative-hynoptics, hallucinogens, and ethanol. The self-administration of drug combinations will be compared to the self-administration dose-effect curve for each drug alone. In addition, other studies on the interactions of drugs of abuse on food-reinforced responding to determine the rate-dependent effects on the drug combination, compared to the effects of each drug alone. These studies will provide both quantitative and qualitative information on the interaction of drugs of abuse with narcotic self-administration. This information is currently not available. The results of these studies may provide a new insight into the etiology and treatment of alcoholism in methadone maintenance patients on untreated narcotics addicts.